Electricity + Control October 2015

EARTHING + LIGHTNING PROTECTION

Self supporting air-termination rod.

Lightning protection components are subject to natural weathering and exposure to corrosion.

The mechanical properties of all lightning protection conductors must be tested and observed. Additional tests like the bending test and the current carrying ability must also be applied and observed. Data sheets for all conductors should be available on request by all lightning protection manufacturers and installers. In order to be able to create long earth electrodes (3 m to 30 m long), the earth electrodes are extendable via rod couplings. Both the earth electrodes and the rod couplings are subject to testing in terms of the standards. SANS / IEC 62561-2 [2] specifies the requirements for earth electrodes such as material, geometry, minimum dimensions as well as mechanical and electrical properties. The coupling joints linking individual rods are weak points, for this reason, additional mechanical and electrical tests have to be performed to test the quality of the coupling joints. Generally earth electrodes are made of the following materials: • Hot dipped galvanised steel rods

arise as soon as the lightning current flows through them. In order to test the worst case, not only the different conductor combinations but also the material combinations must be tested. Possible material combinations for air-termination systems, down conductors and for connection to structural parts. Steel Aluminium Copper StSt Titanium Tin Steel (St/tZn) Yes Yes No Yes Yes Yes Aluminium Yes Yes No Yes Yes Yes Copper No No Yes Yes No Yes StSt Yes Yes Yes Yes Yes Yes Titanium Yes Yes No Yes Yes Yes Tin Yes Yes Yes Yes Yes Yes The testing of the clamps must comprise all of the possible conduc- tor combinations and the aged as well as the new components. The clamp connections are then subjected to lightning current impulses of 10/350 μs wave shape with 50 kA and 100 kA being applied to each specimen. The clamps must show no signs of damage and the transition resistance must not exceed 2,5 m Ω . The result of the tests showed that two types of clamps are applicable: • Heavy Duty (H) = 100 kA (lightning protection level I and II) • Normal Duty (N) = 50 kA (lightning protection level III and IV) The selection of the right type of clamp should be done by the whether there is any current division before the clamp location. This test pro- cedure must be performed for all types of connection components. Detailed test reports should be made available for each lightning protection designer and should be based upon various factors like lightning protection level or lightning protection component. Test procedure for electrodes The SANS / IEC 62561-2 standard places special requirements on conductors such as air termination conductors, down conductors and earthing conductors. These requirements are: • Mechanical properties (minimum tensile strength, minimum elongation) • Electrical properties (max. Resistivity) • Corrosion resistant properties (via artificial ageing)

• Stainless steel rods • Solid copper rods • High tensile, low carbon copper clad rods

By far the majority of rods that are installed are the copper clad rods. In order to comply with the requirements of the standards, the minimum copper cladding shall be as follows:

99,9% Pure electrolytic copper clad to a minimum thickness of 250 microns (0,250 mm) = Grade ‘A’

Test in salt mist chamber.

Electricity+Control October ‘15

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